Thermally-activated vapor etchant for InP

ABSTRACT

Vapor from liquid ethylene dibromide (EDB) functions in a manner superior  anhydrous HCl for in situ gas phase etching of InP substrates in Metalorganic Vapor Phased Epitaxy (MOVPE). The etch rate and surface morphology behaviors have been determined for conditions useful as a substrate cleaning step prior to growth of InP and InGaAs epilayers. The thermally activated decomposition and etching are analogous to group III-V semiconductor growth processes; the behavior in different carrier gas mixtures demonstrates dependence on gas phase reactions in the heated vapor above the substrate.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

Successful growth of epilayers on InP single crystal substrates requirescareful cleaning procedures to remove surface contaminants, oxides andmechanical damage. The specific procedures vary with the investigatorand the epitaxial growth techniques; however, the substrate preparationsteps typically include (1) chemo-mechanical polishing of the substratesurface to obtain a flat, damage-free growth interface, (2) chemicaletch of interface oxides immediately prior to growth sometimes includingremoval of some depth of the InP to eliminate residual mechanicaldamage, and (3) an in situ etch of the surface in the growth chamber toprovide a freshly exposed surface in the controlled growth environment.In the chloride and hydride vapor-phase growth techniques, surface etchconditions can be provided by the growth vapors before layer growthconditions are established. However, in metalorganic vapor-phase epitaxy(MOVPE) an etch-mode cannot occur from the growth constituents so aseparate etchant species must be introduced.

The use of anyhdrous HCl has been reported in two relatively recentarticles by M. Razeghi, M. A. Poisson, J. P. Larivain and J. P.Duchemin, in their article in Journal of Electronic Materials 12 (1983)page 371 and J. S. Whiteley and S. K. Ghandhi in their article appearingin Journal of Electro Chemistry Society 129 (1982) 383. This use ofanyhdrous HCl is a necessary etchant step for successful MOVPEpreparation of the alloy semiconductor InGaAs on InP. With in situetching of the InP substrate it is possible to achieve specular layersurfaces. HCl however is a very difficult vapor to handle. The slightesttraces of moisture accelerate corrosion of metal gas regulators, flowcontrollers, valves and tubing. Elastomer O-ring seals are particularlyvulnerable to the cross-diffusion of HCl in the delivery lines with thewater vapor outside. Frequently, the lifetime of HCl gas-controlledcomponents is short. A hazard represented by the HCl is its 630 psigcylinder pressure and potential dispersion of the corrosive toxic gasinto the environment should its pressure regulator fail.

A good alternative to etchants stored under high pressure is to pass acarrier gas through an etchant liquid whose vapor pressure is sufficientto provide a useful gas concentration. Vapor etching of GaAs substratesfor MOVPE growth is reported with AsCl₃ as the etchant. A thoroughdiscussion of this phenomena is set forth in the article by R. Bhat andS. K. Ghandhi, in the Journal of the Electro Chemical Society 124 (1977)1447. The AcCl₃ decomposition provides a higher purity source of HCl andcompressed anhydrous HCl. Decomposition of gaseous methyl bromide, CH₃Br has been reported as photochemical etchant for GaAs and InP in thearticle by D. J. Ehrlich, R. M. Osgood and T. F. Deutsch appearing inApplied Physics Letter 36 (1980) 698. The gaseous methyl bromide shouldalso be useful as a thermally-activated etchant; however, it has thedisadvantage of a 1.83 atmosphere vapor pressure requiring a pressurizedcylinder.

Thus there exists in the state-of-the-art a continuing need for anetchant for an indium phosphide substrate in the form of a readilyavailable liquid having a convenient vapor pressure that lends itselffor use at room temperature and is not overly corrosive, innon-flammable and doesn't react with moisture in air and further lendsitself to being readily controlled.

SUMMARY OF THE INVENTION

The present invention is directed to providing a method for etching anInP semiconductor substrate to assure the removal of surfacecontaminants, oxides and mechanical damage. Ethylene dibromide isvaporized at a manageable vapor pressure and carried in a pure carriergas at room temperature past a preheated substrate. Heating an InPsubstrate and flowing vaporized ethylene dibromide over it causes theetching of the substrate. A substrate temperature of greater than 650°C., and preferably 675° C. assures a satisfactory etching. Hazards arereduced with the safer ethylene dibromide.

A prime object of the invention is to provide an improved method ofetching InP substrates.

A further object is to provide for an improved method for etching an InPsubstrate relying upon ethylene dibromide.

Still another object is to provide for an ethylene dibromide etchantadapted for cleaning InP substrates that avoid the problems associatedwith more highly corrosive etchants.

Still another object is to provide for an improved etchant of InP thatreduces the problems associated with excessive pressures of etchants.

Still another object of the invention is to provide for an improvedetchant of InP substrates that is non-flammable and does not react withambient moisture.

Still a further object is to provide for an improved etchant operable inan atmospheric pressure reactor having gas flow rates that arecontrolled in a pure carrier gas ahead of a liquid source bubbler.

These and other objects of the invention will become more readilyapparent from the ensuing specification when taken with the claims andthe subject matter of the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 sets forth a schematic representation of the apparatus associatedwith the improved method of etching InP substrates of this invention.

FIG. 2 is a depiction of InP (100) EDB etch-rate temperature-dependencein H₂ carrier gas.

FIG. 3 is a representation of InP, 3-off (100) toward (110), EDBetch-rate temperature-dependence in H₂ carrier gas.

FIG. 4 shows InP (100) EDB etch-rate temperature-dependence in 25% of H₂plus 75% N₂ carrier gas.

FIG. 5 is a depiction of InP (100) EDB etch-rate temperature-dependencein 25% H₂ plus 75% He carrier gas.

FIG. 6 shows InP (100) etch-rate dependence on the concentration ofethylene dibromide (EDB) vapor in H₂ carrier gas. Total gas flow =2 SLm;time =5 minutes; t=650° C.; PH₃ =5.5×10⁻³ atm.

FIG. 7 shows InP (100) EDB etch-rate dependence as a function of thesquare-root of the H₂ carrier gas velocity. Gas flows range from 1 to 6SLM; partial pressures of the reactants are maintained constant;EDB=1.3×10⁻⁴ atm.; PH₃ =5.5×10⁻³ atm.

FIG. 8 shows InP (100) EDB etch-rate dependence on time.

FIG. 9 is a depiction of InP (100) EDB etch-rate dependence on carriergas species for mixtures of hydrogen with nitrogen and helium. Total gasflow=2 SLM; EDB=1.3×10⁻⁴ atm.; T=650° C.; PH₃ =5.5×10⁻³ atm.

FIG. 10 shows the improved method of etching employing ethylenedibromide vapors.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The essence of the invention relies upon the selection of an organichalide, ethylene dibromide, CH₂ BrCH₂ Br, (EDB) also called dibromoethane, as an alternative halide etchant on the basis of a number ofpractical considerations. Ethylene dibromide, also known as glycoldibromide is a readily available liquid. It has a molecular weight of187.88, a boiling point of 131.4° C., a specific gravity of 2.18, avapor density of 6.5 (times air), a melting point of 9.3° C. and a vaporpressure at 20° C. of 12 mm of mercury. The vapor pressure makes itconvenient for using the liquid at room temperature and it is much lesscorrosive at room temperature than HCl and HBr. It is non-flammable anddoesn't react with moisture in air in an atmospheric pressure reactorthe gas flow rates can be controlled in the pure carrier gas ahead of aliquid source bubbler.

It is important to bear in mind that ethylene dibromide in both theliquid and the vapor state are toxic so that appropriate handlingprocedures are used. As mentioned above it is non-combustible and at 20ppm PEL, a permissible exposure limit average over an 8-hour work shiftis tolerable. While a 50 ppm maximum peak exposure for 5 minutes duringan eight hour work shift may be experienced without adverse reactions.Its odor is detectable above 10 ppm however there are poor warningproperties. Ethylene dibromide is incompatible with the chemicallyreactive metals sodium, potassium, calcium, zinc, manganese and powderedaluminum. It is also imcompatible with liquid ammonia and strongoxidizers as well as the hazardous decomposition produced HBr, Br, andcarbon monoxide. It will attack some plastics and rubbers and slowlydecomposes when exposed to light. Human handlers of ethylene dibromidemay experience blisters if the liquid contacts the skin and evaporationof it is delayed. Inhalation of ethylene dibromide fumes causes delayedpulmonary lesions and prolonged exposure may result in lever and kidneyinjury. It is suspected carcinogen. However, in view of the risksoutlined above the use of ethylene dibromide as an etchant is less thansome of the conventionally used alternatives.

Referring now to FIG. 1 of the drawings the improved etchant is used ina standard MOVPE system having an enclosure 10 with transparent windowsthat contain MOVPE reaction chamber 15. The reaction chamber can be nomore than a cylindrically shaped quartz container of sufficient size tocontain a graphite susceptor slab 16 that is coupled to and RF inductionheater 17. A temperature control system for the RF indiction heater isprovided to assure that the susceptor heats a substrate 18 to the propertemperature for subsequent circuit building procedures. The substrate inthis case is InP and as a condition prior to subsequent fabricationsteps needs to have its surface etched clean to further assure thepurity of reactive processes and to withstand the attendant temperatureextremes which approach 1000° C. A gas controlled system 20 is used tocontrol the pressure, temperature and volume of carrier gases such asnitrogen or hydrogen or combinations thereof along with the ethylenedibromide etchant. The carrier gases and ethylene dibromide are fed tothe reactor chamber 15 via an appropriate fitting 21 which reaches fromthe gas control system to the chamber.

The MOVPE reactor chamber induction heater with temperature controlsystem and gas control system are well established in the art toaccomplish the MOVPE process. The gas control system additionallyregulates the temperature, pressure and volume of arsine and phosphine,trimethyl indium, trimethyl gallium used to grow InP and InGaAsepilayers for a variety of semiconductors such as field effecttransistors and photodetectors. The widely used systems are suitablymodified to accommodate the ethyline dibromide in a manner to bedisclosed below to improve the etching process without the riskattendant the use of the conventional etchants.

The introduction of ethyline dibromide vapor into the MOVPE reactor isachieved by use of a pyrex gas scrubbing bottle interconnected to thegas control system with stainless steel tubing and O-ring seals to theglass. Hydrogen or nitrogen gas controlled by a mass flow controller inthe gas control system is bubbled through room temperature liquid EDBand transported to the reactor chamber. The pyrex gas scrubbing bottletubing and seal were not shown and were grouped in the gas controlsystem since such expedients are well known in the art and theirinclusion here would only belabor the obvious.

A series of runs has been made to determine the etchant behavior of EDBon polished pieces of (100)-oriented, FE-doped InP to characterizetemperature dependence, EDB concentration dependence, total gas flowdependence, time dependence, and dependence on the species of thecarrier gas. Polished substrates were cleaned before use with potassiumhydroxide for ten minutes or longer followed by a 1-minute 1%bromide/methanol etch, a methanol rinse than blown dry and filterednitrogen gas. The substrates are immediately weighted and placed in theMOVEP chamber. The etching conditions using the ethylene dibromide weremonitored over a range of temperatures and gas flow conditions similarto those used for epilayer growth. The reactor chamber 15 is ahorizontal 1"×1" cross-section tube with a 1/4" high ×1" wide ×11/2"long graphite susceptor 16 resting on the bottom. RF induction heatingfrom heater 17 is used with a thermo couple inserted in the susceptor tocontrol the temperature. All gases are controlled with mass flowcontrollers in an all stainless steel distribution system 20. In thecarrier gases hydrogen is palladium purified and the nitrogen is fromvaporized LN₂. The exhaust gases from reactor pass through a duct 22that feeds the exhaust gases through activated charcoal to removeorganic and hydride resitual vapors.

The etching times are typically about 5 minutes; the total gas flow isabout 2 SLM (gas velocity in the cold portion of the chamber of 5.2 cmper second); and temperatures span from 400°-750° C. with most of theresults at 650° C. A partial pressure of PH₃ was used to inhibit InPthermo decomposition. The two major results examined for optimizedperformance are the etch rate and the surface morthology.

The etch rate is determined by the weight-loss of the InP substrate 18using an analytical balance with 1-microgram resolution. The InP used toverify this concept consisted of various-sized small scraps with (100)surface areas of 15-30 square millilmeters. To estimate the thicknessremoved by the etchant the loss from the substrate edges also wasconsidered. For those small pieces the edges composed approximately 30%of the exposed InP surface. The thicknesses removed was determined byassuming no weight loss from the substrate surface in contact with thegraphite susceptor, and assuming the etch rate of the (110) edges to bethe same as the (100) polished surface.

The temperature dependence of etch rate for EDB-InP vapor etching isapparent by a series of runs with all parameters but temperatureconstant. The exception to this was an increase in PH₃ concentration athigh temperatures to prevent surface degradation. It was determinedhowever, that the etch rate data is independent of PH₃ fraction. Theetch time was consistently five minutes. The EDB concentration 1.3×10⁻⁴atm. The total gas flow 2 SLM and the PH₃ concentrations 5.5×10⁻³ atm.or greater. The etch rate temperature dependence has been determined forfour different conditions. FIG. 2 shows the log of the etch rate vs.reciprocal absolute temperature for (100) oriented InP in H₂ carriergas. FIG. 3 shows the similar data for 3% -off (100) toward(110)-oriented InP in H₂ carrier gas; and FIGS. 4 and 5 show rate datafor (100) InP in 25% H₂ +75% N₂ and 25% H₂ and 75% He, respectively. Thelog rate vs. 1/T format is usual for thermally activated processes andis used here for easy comparison with other etching and growth processeson III-V materials. The data are virtually identical for both (100) and3% -off (100) InP in H ₂ carrier gas; and the qualitative dependence ontemperature is the same in gas mixtures of H₂ with He and N₂.

The EDB etch rate temperature dependence is similar to both etching andgrowth behavior of GaAs. These phenomena were predicted in the abovecited articles in the Journal of Electro Chemical Society 124 (1977)1447 and Applied Physics Letters 36 (1980) 698. The exponential increaseof rate with temperature below 500° C. is typical of a surface processunder kinetic control; and the apparent activation energy of 38 K cal/mois tyupical of such processes, D. W. Shaw "Mechanisms in Vapor Epitaxyof Semiconductors" Crystal Growth Theory and Techniques Vol. I Ed. C. H.L. Goodman (Plenum Press, London, 1974). A further argument for controlof the etch by surface kinetics at the lower temperatures is seen in thetemperature dependence of (100) morphologies. For H₂ carrier gas theetch pits at 550° C. and lower have distinct crystallographicorientation and faceting typical of etch rates limited by the surfacekinetics.

For the 700° C. to 750° C. range where etching is mass transport limitedthe rate is controlled by processes away from the substrate surface. Theinsensitivity to crystal surface chemistry reduces the etch pitformation however, at these temperatures a degree of thermal pittingoccurs regardless of increased PH₃ concentrations. For the 575° C. to600° C. regime the etch pits are seen to be shallow and less defined bycrystallographic facets. The absence of strong crystallographicdependence weakens any argument that this regime is dominated solely bysurface kinetic processes. Also there are some specimens etched in thisregime which showed absence of etch pits. The edges of samples whichcorrespond to the outer edge of the polished wafer typcially are free ofpits. The outer surface of the wafer has been polishd and etched morethan the central region, and as a result, the surface is slightly curvedso it is no longer parallel to (100). The use of substrates oriented 3°-off (100) toward (110) results in dramatic reduction in etch pitfeatures with no difference in the etch rate. The improved etchmorphology is consistent with observed improvement in CVD III-V layermorphology when substrates are misoriented two or three degrees from(100), see the A. E. Blakeslee, "Effects of Substrate Misorientation inEpitaxial GaAs", Transactions of the Metallurgical Society AIME 245,577(1969).

The dramatic effecxts of surface orientation may explain observedmorphology variations for some samples etched under identicalconditions. The remaining data discussed below are for nominally (100)InP surfaces, however, the exact orientations used in this study werenot controlled. This introduces an element of caution in interpretinganomolies in the morphology data presented in the figures.

The dependence of etch rate on EDB concentration is shown in FIG. 6. TheEDB concentrations were determined by the flow rate of H₂ carrier gas atrates from 0-100 sccm (i.e., vapor pressures up to 6.5×10⁻⁴ atm). Withinthis range the etch rate is linear with concentration. The severity ofsurface pitting increases with concentration. This is attributed to theetchant concentration rather than the depth of the etch since it hasbeen noted that deeper etches, by using long times and slow rates, showsmoother surfaces. Apparently increasing the EDB concentration overcomesthe boundary layer diffusion limits so that the etch process becomesmore controlled by surface kinetics, thus the increased pitting.

The effect of gas velocity on the EDB etching was assessed by increasingthe total flow with the partial pressures of the EDB and PH₃ heldconstant. In th confines of a fixed geometry chamber this is equivalentto increasing the velocity of a gas of constant composition. The etchrate for diffusion-controlled mass transport should, according to E. C.Eversteyn, P. S. Severin, C. H. J. van der Brekel and H. L. Peak in "AStagnant Layer Model for the Epitaxial Growth of Silicon from Silane ina Horizontal Reactor" Journal of the Electro Chemical Society 117,925(1970) be proportional to the square root of the velocity correspondingto a reduction in the stagnant "boundary layer" at the InP surface. Thedata of FIG. 7 indicates this general behavior. A departure of thesquare root dependence at high velocities is expected because conditionsare approached where the boundary layer becomes thin and kineticprocesses again influence the etch rate. These data seem to confirm thatin FIGS. 2-5 at 600° C., the rates are primarily diffusion controlledwith a velocity dependent boundary layer thickness. No difference in thesurface morphologies was observed for the change in gas velocity.

The dependence of EDB etch rate on time in H₂ carrier gas is shown inFIG. 8 to be linear and no significant changes in surface morphologywith time were observed over the range of temperature from 400° to 750°C. The etch pit characteristics do not change, although the surfaceroughening increases.

The introduction of nitrogen and helium as a fraction of the carrier gasshows a definite influence on the etch rate as seen in FIG. 9. Thermalconductivity and its effect on temperature gradients and the volume ofheated gas over the susceptor are of major importance; however, it isalso apparent that the gas phase kinetic equilibrium and/or thevapor/solid surface kinetics would be changed by reduction of H₂ partialpressure. No dramatic changes in the surfaces are observed; however,comparison of morphologies for the gas compositions shows some subtledifferences.

Phosphine was necessary in some minimum concentration to maintain smoothsurfaces. The etch rates of EDB, however, are independent of the PH₃concentration, even for cases where the surface showed severe thermaldegradation. This insensitivity to the phosphorus suggests that it isthe action of the etchant in the In that limits the rates. InsufficientPH₃ was evident from the presence of uniformly distributed pits and Indroplets or more severe roughening. The minimum PH₃ partial pressuresfound necessary for good InP surfaces in a 2 SLM total gas (H₂ flow) at650° C. PH₃ is at 5.5×10⁻³, at 675° C. PH₃ is at 1.10⁻² atm, for 700° C.PH₃ is 1.38×10⁻², at 725° C. PH₃ is 1.67 at 10⁻² and at 750° C. PH₃ isat 2.20⁻² atm. For all temperatures below 650° C. the PH.sub. 3 wasmaintained at 5.5×10⁻³ atm, at temperatures 700° C. and above thesurfaces have a distribution of fine thermal etch pits regardless of howmuch PH₃ is introduced.

An analogy between the etchant behavior on InP substrates is made togrowth behavior. Etching times are about 5 minutes compared to about 30minutes or longer for layer growth, the growth chamber walls stay cleanand the etchant is much cheaper than the metal alkyls used for MOVPE.Etching also provides information for optimizing the surfaces on whichlayers are to be grown, and by inference, the behavior of thevapor/solid interactions expected during growth.

A general description of vapor-phase growth/etching in open flow systemsas a sequence of process steps has been outlined in the above citedarticle by Shaw appearing in Crystal Growth and Techniques. The processrates are controlled by (1) the supply of reactants into the chamber,(2) the mass transfer of these reactants and their byproducts to andfrom the vapor stream to the substrate surface, and (3) the kinetics ofthe reactions at the substrate surface. Whichever of these steps isslowest will control the process rate.

In pyrolytic deposition techniques, such as used in silicon layer growthand in III-V MOVPE layer growth, the reactant gases are introduced andtransported at room temperature in a cold wall quartz chamber.Decomposition and reaction of the gases occurs by thermal activationfrom the heated substrate and its supporting susceptor. Deposition bypyrolysis is frequently modeled simply as a non-equilibrium surfacereaction with the rates controlled by the surface kinetics limited undersome conditions by the diffusion of the vapors across a stagnantboundary layer. It is realistic to consider that at least some input gasspecies will decompose in the heated vapor space above the susceptor aswell as at the substrate surface, and the rate limitations can resultfrom the gas phase reactions as well. The vapor/solid interfaceinteraction would include a whole family of generated vapor species inquasi-equilibrium and the growth or etching is driven by departure ofequilibrium of the vapor with the solid.

An analysis of pyrolytic growth based solely on calculatedthermo-dynamic vapor equilibrium and gas flow hydrodynamics (exclusiveof surface kinetics) has been modeled for silicon growth from silane byColtrin et al, see "Mathematical Model of the Coupled Fluid Mechanicsand Chemical Kinetics in a Chemical Vapor Deposition Reactor" aboveappearing in Journal of the Electro Chemical Society 131,425 (1984). Thearticle assumes that the reaction zone is in the vapor with the ratescontrolled by the gas-pase kinetic processes. In this anslysis thecoupled fluid mechanics and chemical kinetics predict the gas-phasetemperature, velocity and chemical species concentration profiles; thedeposition rates agree with experimental results.

An important feature of the Coltrin et al article is that thecalculations demonstrate the rate dependence on gas conductivity. Thevapor etch behavior of EDB on InP is consistent with predictions of thismodel. If the EDB etch rates are controlled by gas-phase decomposition,then the shape and position of the reaction zone will be determined byboth heat transfer away from the susceptor and mass transfer processesin the gas phase. For nitrogen carrier gas the volume of heated gasabove the susceptor will be much smaller than the hydrogen or for heliumbecause of the much lower thermal conductivity. The etch rate dependenceon gas species in FIG. 9 is consistent with this behavior. The EDB etchrate appears to be related to the extent of the gas phase reactions. Asthe heated zone volume increases by using H₂ or He gas, more reactant isavailable from decomposed EDB. The increased dimensions of the zone donot cause problems for mass transfer of the reactant because the gasdiffusivity behavior is identical to the thermal diffusivity responsiblefor establishing the greater reaction zone volume. The gas phase kineticprocess will likely depend on the hydrogen partial pressure and mayexplain the increase in etch rate as helium is introduced.

Comparison of the etch rate temperature dependence data of FIG. 2 for H₂carrier gas with FIG. 4 for 25% H₂ and 75% N₂ shows the rate dependencesto be consistently a factor of two different over the entire temperaturerange. The effect of different carrier gas is to change the supply ofreactant accessible to the InP surface from the gas phase. Thetemperature dependence of the etch-rates is unchanged. Both kinetic anddiffusion rate-controlled regimes are expected to show first orderdependence on the etchant concentration.

The scatter in etch rate data obscures the exact shape of the curves inFIGS. 2, 3, 4, and 5; however, the general trends are consistent. Someof the scatter results from arbitrary differences in shapes and sizes ofthe InP specimens. The data of FIG. 5, however, were taken on nearlyidentical pieces of InP. From these more consistent data a distinctplateau in the etch-rate temperature-dependence is seen from 500° C. to550° C. This suggests that there may be two different activatedprocesses that contribute to the etching, one below 500° C. and theother dominating the etch above 550° C. There is a hint of this plateauin H₂ carrier gas of FIGS. 2 and 3; however, in the H₂ and N₂ carriergas of FIG. 4, the scatter is too great to tell. The tube geometry andgas velocities were chosen to provide lamillar flow which is thesimplest flow configuration to analyze since convective flow is limitedparallel to the substrate and the mass transport to and from the gasstream is by diffusion. The rectangular tube cross-section with heatingat the bottom is a stable configuration for lamellar flow withsufficiently high gas velocities, as demonstrated by L. J. Giling. in"Gas Flow Patterns in Horizontal Epitaxial Reactor Cells Observed ByInterference Holography" Journal of the Electro Chemical Society 129,634(1982). It has been reported however that the flow for lowerconductivity N₂ and Ar is much less stable than for H.sub. 2 and He. Theincreased scatter in etch data for H₂ and N₂ is likely due to convectiveinstabilities perturbing the uniform distribution of etchant.

Referring to FIG. 10 of the drawings there is seen the improved processin method for etching an InP substrate to assure the removal of surfacecontaminants, oxides and mechanical damage. Heating 30 the InP substrateand the vaporizing 35 of ethylene dibromide and the subsequent flowing40 of the vaporized ethylene dibromide over the heated InP substrateassures the etching thereof. Mounting 31 the substrate on a susceptorand heating 32 the susceptor assures that the InP substrate is heated toa temperature of 650° C. or preferably to a temperature of 675° C. Thestep of vaporizing includes the bubbling 36 of hydrogen or nitrogenthrough the EDB. The step of flowing includes the mixing 41 of H₂ /N₂ orhelium with the vaporized EDB. Optionally introducing 42 PH₃ preventssurface degradation.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:
 1. A method for etching an InP substrate to assurethe removal of surface contaminants, oxides and mechanical damagecomprising:heating the InP substrate; vaporizing ethylene dibromide; andflowing the vaporized ethylene dibromide over the heated InP substrateto assure the etching thereof.
 2. A method according to claim 1 furtherincluding:mounting the InP substrate on a graphite susceptor having athermocouple that is coupled to an RF induction heater to assure theheating of the InP substrate.
 3. A method according to claim 2 in whichthe step of heating includes:heating of a graphite susceptor and mountedInP substrate by an RF induction heater connected to a thermocouple inthe susceptor to a temperature in excess of 650° C.
 4. A methodaccording to claim 3 in which the step of heating is to a temperature of675° C.
 5. A method according to claim 4 in which the etching of the InPsubstrate depends on gas-phase reactions in heated vapor above the InPsubstrate during the step of flowing.
 6. A method according to claim 5in which the step of flowing includes the mixing of the ethylenedibromide with a mixed H₂ and N₂ carrier gas.
 7. A method according toclaim 6 further including:introducing a PH₃ concentration into flowingethylene dibromide to prevent surface degradation.
 8. A method accordingto claim 7 in which the ethylene dibromide has a concentration of about1.3×10⁻⁴ atm. at a total gas flow of 2 SLM with a PH₃ concentration ofabout 5.5×10⁻³ atm.
 9. A method according to claim 5 furtherincluding:introducing a PH₃ concentration into flowing ethylenedibromide to prevent surface degradation.
 10. A method according toclaim 5 in which an H₂ carrier gas is provided.
 11. A method accordingto claim 5 in which a carrier gas of 25% H₂ and 75% N₂ is provided. 12.A method according to claim 5 in which a carrier gas of 75% H₂ and 25%N₂ is provided.
 13. A method according to claim 5 in which a carrier gasof N₂ is provided with He added to influence the rate of etching.
 14. Amethod according to claim 1 in which the rate of etching is dependent ofthe rate of the step of flowing.
 15. A method according to claim 1further including:introducing phsophine into the flowing of ethylenedibromide to maintain smooth surfaces.
 16. A method according to claim 1in which the step of vaporizing includes the bubbling of H₂ gas throughroom temperature ethylene dibromide prior to the step of flowing.
 17. Amethod according to claim 1 in which the step of vaporizing includes thebubbling of N₂ gas through room temperature ethylene dibromide prior tothe step of flowing.